The present invention relates to a dual frequency band transceiver technique particularly adapted for example for a channel mapping solution of dual band OFDM systems.
Wireless communications systems that are currently in development and future generations of wireless systems are targeting high data rate applications. Therefore the utilization of frequency bands in the microwave range and in the mm wave range has been gaining a lot of interest for the recent years. Private (non-licensed) frequency bands of operation offer a wide variety for prosper commercial applications. There are bands available in the frequency range of about 800 MHz, 2.4 GHz, 5-6 GHz, about 10 GHz, 24 GHz and 59-64 GHz, which can be considered more or less as license free frequency bands or ISM (industrial, scientific, medical) bands. These bands usually have power level limitations.
Generally, the different frequency bands can be classified due to different propagation properties in:
a) NLOS (non-line of sight) and LOS (line of sight) communication, and
b) predominantly only LOS (line of sight) communication.
Due to the increased free space attenuation and decreased wall penetration, wireless communication systems operating at higher frequencies (usually greater than 10 GHz) have in general a very limited coverage range. That means a satisfactory communication is only possible in a LOS or highly reflecting short-range scenario. On the other hand operating in the higher frequency ranges gives the advantage to use more frequency resources, which is necessary for wireless broadband applications, and simultaneously the higher frequency range provide for very good channel conditions. Possible applications therefore are professional high quality video transmission in wireless TV studios, high-resolution image transfer in hospitals or general offices and home applications as for example wireless LAN or wireless home network.
All these applications are distinguished by their requirements as mobility, coverage range and data throughput. Therefore generally there is a need for a receiver technique adapted for transmission in at least two different bands, where for example one of the frequency transmission bands should provide for a NLOS transmission and the other one should provide for a LOS transmission. There is also a need for a interoperability with coexisting systems operating in different transmission frequency bands.
In the state of the art, dual band transmission techniques are known. However, according to these known techniques the difference between the two frequency bands is hardly larger than 20% of the central frequency and in the most cases the difference is even less than 5%.
U.S. Pat. No. 5,564,076 discloses a dual mode portable digital radio transceiver for communication via a terrestrial network (first mode) and via a satellite network (second mode) synthesizing a modulation first frequency for modulation of signals transmitted in both modes and a conversion second frequency for demodulation of signals received in the two modes. This known transceiver divides the converted second frequency supplying a conversion third frequency for demodulation of signals received in one of the modes using a signal receive frequency band far away from the other frequency bands used. In the case of transmission the same means transmitting both modes with no duplication of components. Only demodulation frequencies supplied by an oscillator is adjusted to the specific frequency of the transmission mode in use.
GB-A-2 173 660 discloses a paging receiver including a superheterodyne circuit with a mixer for mixing a first frequency received signal from an antenna with a signal from a local oscillator. An intermediate frequency signal of the paging receiver appears at the output of the mixer and either this signal or a second received signal from another antenna at the same frequency as the intermediate frequency signal is further amplified and decoded depending on the setting of a switch. The switch can be automatically responsive to an area wide transmission by causing the on-site reception to be disabled by the operation of an out-of-range warning circuit.
From U.S. Pat. No. 5,640,694 an integrated RF system with segmented frequency conversion is known.
GB-A-2 312 107 discloses a multi-band receiver and quadrature demodulator with selectable local oscillator. Thereby a receiver may receive one of two bands depending on the position of a switch. This intermediate frequency switch is responsive to a switching control signal indicative of which radio frequency bands the corresponding mobile unit is operating for outputting a first intermediate frequency signal corresponding to a first mobile communication system and outputting a second intermediate frequency signal corresponding to another communication system.
EP-A-633 705 discloses a multi-band cellular radio-telephone system architecture. This dual frequency cellular radio-telephone system has different service providers and serving mobile subscribers at first and second distinct frequency ranges, and using frequency conversion techniques to serve both frequency ranges.
However, all these known dual band transceiver are not adapted to a transmission system according to an OFDM Orthogonal Frequency Division Multiplexing technique.
Therefore it is the object of the present invention to provide for a dual band transceiving technique allowing a transmission in two different transmission frequency bands, wherein the technique should be particularly well adapted for a transmission according to OFDM techniques.
The above object is achieved by means of the features of the independent claims. The dependent claims develop further from the central idea of the present invention.
According to the present invention therefore a dual frequency band transceiver is provided adapted to be operated in two different transmission frequency bands, wherein the dual frequency band transceiver comprises a control unit controlling a switching between the first transmission frequency band and a second transmission frequency band, wherein the control unit is adapted to change between a first and a second channel bandwidth correspondingly and simultaneously to the switching between the first transmission frequency band and the second transmission frequency band.
The first and the second channel bandwidth thereby are set to satisfy the following equation:
n*BC1=m*BC2,
wherein BC1 and BC2 are the first and the second channel bandwidth, respectively, and n and m are integers starting with 1.
Particularly the ratio n/m can be set to satisfy n/m=2i, wherein i is a positive or negative integer value including zero.
A switch can be provided upwardly of a frequency converting block, wherein the switch is controlled by the control unit such that selectively either a signal in the first transmission frequency band or the second transmission frequency band is transmitted/received. The dual frequency band transceiver can furthermore comprise a baseband block and at least one antenna wherein the first frequency converting block is connected between the base band block and at least one antenna and is adapted to convert an intermediate frequency output of the baseband block or output by another frequency converting block, and a first transmission frequency band of the dual frequency band transceiver corresponds to the intermediate frequency and a second transmission frequency band obtained as an output signal of the first frequency converting block.
The control unit is adapted to control the switch together with the bandwidth used according to data link control (DLC) data.
The first transmission frequency band can be below 10 GHz and the second transmission frequency band can be higher than 10 GHz.
The first transmission frequency band can be between 5 and 6 GHz and the second transmission frequency band can be 24 GHz, 40 GHz, or 60 GHz.
The base band block is adapted to operate according to an OFDM modulation technique.
The subcarrier spacings of the OFDM system can be identical in the first transmission frequency band and the second transmission frequency band.
The subcarrier spacings of the OFDM system in the first transmission frequency band and the second transmission frequency band alternatively can satisfy the following equation:
xcex94F1/xcex94F2=k*2i,
wherein xcex94F1 and xcex94F2 are the subcarrier spacings used in the OFDM systems in the first transmission frequency band and the second transmission frequency band, respectively, and k is a positive integer value and i is a negative or positive integer value including zero.
This selection allows an effective implementation of the baseband block to process the OFDM signals and/or symbols.
Different antenna systems can be provided to be used, respectively, when the first or the second transmission frequency band is used.
The present invention furthermore relates to a dual band telecommunications device, such as for example a dualband cellular telephone, which comprises a transceiver as set forth above.
According to the present invention furthermore a method for transceiving in two different transmission frequency band is provided. Thereby a switching between the first transmission frequency band and a second transmission frequency band is controlled. Correspondingly and simultaneously to the switching between the first transmission frequency band and the second transmission frequency band it can be changed between the first and the second channel bandwidth.